I wore one for 3-4 hours last week, and it was fine. As far as effort to breathe, it was tight through my nose, but not a problem through my mouth. I didn’t notice it making me feel weird. It was more effort to resist the urge to touch it. After awhile I did get used to it, and that urge passed.
I only had to walk about two blocks, and then another two blocks later, but most of the time I was sitting in a chair. The biggest problem for me is that it compressed my nose enough to make nose breathing feel restrictive. So, I was mostly a mouth breather in my mask. I did adjust the mask for a few minutes in the car (I didn’t touch it once I was in the dirty zone), to find a position that was still sealed, but not completely squashing my nose. Anyway, yeah, it was uncomfortable, but I did get used to it.
But also, you need to check: some masks are supplied with the filters sealed: you have to unpack them before the mask is used. And sometimes when the filters are replaced, they aren’t replaced correctly and you can’t breath through them.
Mask don’t go well with glasses as you can’t wear either over the other. I tried and every time I’d exhale my lenses would fog. Also when I took it off the rubber bands had driven the frame into the bridge of my nose so badly it (my nose) hurt for the rest of the day.